docs: def check_none(data, moban_file):
      """
      check whether the yaml data has empty value such as:
      """
      if isinstance(data, dict):
          for k, v in data.items():
              if check_none(v, moban_file) is None:
                  loc = data.lc.key(k)
                  raise exceptions.MobanfileGrammarException(
                      constants.ERROR_MALFORMED_YAML
                      % (moban_file, loc[0] + 1)  # line number starts from 0
                  )
      elif isinstance(data, list):
          for i, x in enumerate(data):
              if check_none(x, moban_file) is None:
                  loc = data.lc.item(i)
                  raise exceptions.MobanfileGrammarException(
                      constants.ERROR_MALFORMED_YAML % (moban_file, loc[0] + 1)
                  )
      return data